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authorKrishnan Parthasarathi <kparthas@redhat.com>2013-04-15 15:55:28 +0530
committerVijay Bellur <vbellur@redhat.com>2013-04-17 05:46:09 -0700
commit1787debc1b6640e15a02ccac4699b92affb2bb14 (patch)
tree85a84c7d2b3157956a2cf80b30fcd903116433a9 /xlators/mgmt/glusterd/src/glusterd-rpc-ops.c
parent63098d9ff8dcfc08fd2ed83c62c4ffb63fc2126f (diff)
syncenv: be robust against spurious wake()s
In the current implementation, when the callers of synctasks perform a spurious wake() of a sleeping synctask (i.e, an extra wake() soon after a wake() which already woke up a yielded synctask), there is now a possibility of two sync threacs picking up the same synctask. This can result in a crash. The fix is to change ->slept = 0|1 and membership of synctask in runqueue atomically. Today we dequeue a task from the runqueue in syncenv_task(), but reset ->slept = 0 much later in synctask_switchto() in an unlocked manner -- which is safe, when there are no spurious wake()s. However, this opens a race window where, if a second wake() happens after the dequeue, but before setting ->slept = 0, it results in queueing the same synctask in the runqueue once again, and get picked up by a different synctask. This is has been diagnosed to be the crashes in the regression tests of http://review.gluster.org/4784. However that patch still has a spurious wake() [the trigger for this bug] which is yet to be fixed. BUG: 948686 Change-Id: I51858e887cad2680e46fb973629f8465f4429363 Original-author: Anand Avati <avati@redhat.com> Signed-off-by: Krishnan Parthasarathi <kparthas@redhat.com> Reviewed-on: http://review.gluster.org/4833 Reviewed-by: Vijay Bellur <vbellur@redhat.com> Tested-by: Gluster Build System <jenkins@build.gluster.com>
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